1. Field of the Invention
The present invention relates generally to methods and apparatus for performing riserless drilling from an offshore platform, and more particularly, to methods and apparatus for performing riserless drilling using a lightweight drill string, and still more particularly, to methods and apparatus for drilling an offshore well from a platform using a lightweight, small diameter, continuous drill string thereby enabling the use of comparatively smaller diameter pipe components and a smaller platform versus conventional methods.
2. Description of the Related Art
Offshore hydrocarbon drilling and producing operations are typically conducted from a drilling rig located either on a bottom-founded offshore platform or on a floating platform. A bottom-founded platform extends from the seafloor upwardly to a deck located above the surface of the water, and at least a portion of the weight of the platform is supported by the seafloor. In contrast, a floating platform is a ship, vessel, or other structure, such as a tension-leg platform, for example, in which the weight of the platform is supported by water buoyancy.
In recent years, exploration and production of offshore crude oil and natural gas reservoirs has expanded into ever-deeper waters. Successful drilling operations have been conducted in deep waters of at least 3,000 feet deep, and ultra-deep waters ranging from 5,500 to 10,000 feet deep. With increasing water depths, drilling operations conducted from moored or dynamically positioned floating platforms have become more prevalent since economic and engineering considerations militate against the use of bottom-founded drilling platforms commonly used in shallow water.
Regardless of whether a bottom-founded or floating platform is used, conventional methods for drilling an offshore well are similar. In such operations, the platform supports a drilling rig and associated equipment, and must include adequate deck space for pipe storage and handling. The platform is positioned near the wellsite, and a drill string, typically formed of jointed steel pipe that is threaded together one joint at a time, conveys a bottom-hole drilling assembly (BHA) from the platform to the seafloor. A drill bit, disposed at the terminal end of the BHA, drills the well.